Re: cardinal fish. The flash makes them appear more pale than they looked in real life. It was a night dive, and I think it is difficult to discern color under lights sometimes. The width of the band at the base of the tail makes me think these were barred, not pale cardinalfish, but who knows.

Re: emerald parrotfish. I am wondering if some of the fairly nondescript small parrotfish we see in shallow water are juv and initial phase emeralds. I think I have a pretty good search image for juv/init redband and greenblotch, but many of the others that don't fit these species descriptions could maybe be emerald or bucktooth? Are they common in shallow water, sand and grass flats? The photo here is one of the few pattotfish I've seen that really looks like a terminal phase emerald.

Re: hamlets. I don't know what to make of some of these. I only got a few pictures, but among the populations of obvious barred, yellowbelly, butter, and goldens hamlets, there are a bunch of individuals that look like a mash-up of these four species.

I would say barred cardinalfish- both lines are thin, they can look very pale and pearly..

Emerald parrotfishes are a group with a different lifestyle- prefer cooler weedy habitats, rarely found on "nice" reefs, especially out on offshore islands, not sure where Corn Islands fall in that spectrum. I would think those are greenblotch if it were on a nice coral reef.